Others have good advice. If you are a morning person and depending on your kids' sleep patterns, you could maybe get up and out while they are still asleep, and enjoy a walk/bike/run whatever (or stay home and enjoy that, if that works for you). If you're not a morning person (I'm not), maybe an evening out -- my DH and I each take one evening when we go out on our own and the other person is entirely responsible for the kid (we have just 1), full stop. It's remarkably blissful, in my experience (ah, the joy of NOT being responsible for bedtime). I've done everything from take myself to a nice supper to go for a swim at the local public pool. I do try to stay out until the kid is fast asleep, because -- the joy of not being responsible for bedtime!
Is getting a job in an office an option? I know that's a heretical suggestion in these parts and of course depending on what it would involve, might or might not improve alone time, but really, you could not have paid me enough to be a SAHM when mine was little. I need away time (and he needed time with other kids, which daycare provided). But I am fortunate to have pretty good earning power and to live in a place that has good childcare options available (and while I didn't count this as good fortune -- I wanted another, having just one to pay for childcare for obviously made doing so much less costly, also).